#include <iostream>
#include <list>


struct ListNode {
    int val;
    ListNode *next;
    ListNode() : val(0), next(nullptr) {}
    ListNode(int x) : val(x), next(nullptr) {}
    ListNode(int x, ListNode *next) : val(x), next(next) {}
};

class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
    ListNode* head = nullptr, *tail = nullptr;
        int carry = 0;
        while(l1 || l2) {
            int n1 = l1 ? l1->val : 0;
            int n2 = l2 ? l2->val : 0;
            int sum = n1 + n2 + carry;
            if(!head) {
                head = tail = new ListNode(sum % 10);
            }
            else {
                tail->next = new ListNode(sum % 10);
                tail = tail->next;
            }
            carry = sum / 10;
            if(l1) l1 = l1->next;
            if(l2) l2 = l2->next;
        }
        if(carry > 0) tail->next = new ListNode(carry);
        return head;
    }
};

int main() {
    return 0;
}